TR-34: Disinfection of Newly Constructed Polyethylene Water Mains

Effects of Disinfection on Newly
Constructed Polyethylene
Water Mains
TR-34 / 2001 B
Plastics Pipe Institute
www.plasticpipe.org
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Foreword
This report was developed and published with the technical help and financial
support of the members of Plastics Pipe Institute, PPI. The members have shown
their interest in quality products by assisting independent standards-making and
user organizations in the development of standards, and also by developing
reports on an industry-wide basis to help engineers, code officials, specifying
groups, and users.
The intent of this technical report is to provide information on the effects of
chlorine disinfection on the durability of PE piping for water systems. The testing
reported herein was conducted on service pipe sizes and on resins in the form of
plaques in accordance with the various test methods employed. At the time the
testing was conducted, high performance PE materials such as PE4710 were not
available. In 2006, PPI established a new program to provide test information on
high performance PE materials, and will update this report when the information
is available.
Tests on piping in this report were conducted on service sizes; however, larger
PE pipes produced to AWWA C901 and AWWA C906 are subject to the identical
water service design criteria and in-service operating stresses. Furthermore,
chlorine resistance tests of other olefin materials such as PEX have
demonstrated that tests of service sizes are representative of larger sizes.
Therefore, the test results herein are expected to be representative of larger
sizes.
This report has been prepared by PPI as a service of the industry. The
information in this report is offered in good faith and believed to be accurate at
the time of its preparation, but is offered without any warranty, expressed or
implied, including WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE. Any reference to or testing of a particular
proprietary product should not be construed as an endorsement by PPI, which
does not endorse the proprietary products or processes of any manufacturer.
The information in this report is offered for consideration by industry members in
fulfilling their own compliance responsibilities. PPI assumes no responsibility for
compliance with applicable laws and regulations.
PPI intends to revise this report from time to time, in response to comments and
suggestions from users of the report. Please send suggestions of improvements
to the address below. Information on other publications can be obtained by
contacting PPI directly or visiting the web site.
The Plastics Pipe Institute
http://www.plasticpipe.org
(Editorial Revisions, February 2007)
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Effects of Disinfection on Newly
Constructed
Polyethylene Water Mains
Table of Contents
1. Introduction 4
2. Scope 4
3. Methods of Chlorination 4
4. Industry Practice 5
5. Test Results 5
5.1 Quick Burst 5
5.2 Sustained Hydrostatic Burst 7
5.3 Tensile and Elongation 9
5.4 Oxidative Induction Time 9
5.5 High Speed Tensile Impact 10
5.6 PENT Testing 11
6. Other Experience 12
7. Chlorine Dissipation Rate 13
8. Conclusions / Recommendations 13
9. References 13
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1. Introduction
Disinfecting of water mains has been a common industry practice for many
years. The first AWWA standard covering this practice was approved in
September 1947 (as 7D.2-1948). In 1986, the designation of the standard was
changed to AWWAC651; the latest revision is ANSI/ AWWA-C651-92. The
standard describes methods of disinfecting newly constructed potable water
mains; mains that have been removed from service for planned repairs or for
maintenance that exposes them to contamination; mains that have undergone
emergency repairs due to physical failure; and mains that, under normal
operation, continue to show the presence of coliform organisms.
Because the chlorine disinfection process puts pipe in contact with a strong
oxidizer, a task group was formed in June 1993, within the PPI Technical
Committee to investigate possible effects of disinfection on the durability of PE
piping in potable water service. While C651 covers all piping materials used in
potable water service, this investigation was confined to polyethylene systems.
Chlorine was the only disinfecting agent investigated; chloramines were not
evaluated. All tests conducted were short term, run at ambient temperature
conditions on pipe samples made from particular polyethylene pipe compounds.
The report is not to be construed as an indicator of the long-term performance of
polyethylene pipe in general, or in the specific user’s environment and operating
conditions.
2. Scope
At the first task group meeting, the following scope was adopted: To investigate
and quantify, if possible, any effects on the durability of PE piping caused by
disinfection per AWWA C651. Exposure times and concentration levels were
chosen to be consistent with the requirements of the standard. Note that the
disinfection practices outside the constraints used in this study (i.e., exposure
time, etc.) may yield different results - e.g., if a contractor leaves a pipe full of
concentrated disinfectant for 6 months.
3. Methods of Chlorination
Three methods of chlorination are explained in AWWA-C651: tablet, continuous
feed, and slug. The tablet method is intended to give an average chlorine dose of
approximately 25 mg/L, and precautions shall be taken to ensure that air pockets
are eliminated and the water shall remain in the pipe for at least 24 hours. If the
water temperature is less than 41°F (5°C), the water shall remain in the pipe for
at least 48 hours ; the continuous feed to give a 24 hour residual of not less than
10 mg/ L; and the slug method to give a 3 hour exposure of not less than 50
mg/L free chlorine. .. Residual free chlorine In the slug method, shall be
measured as it moves through the main. If at any time it drops below 50 mg/ L,
the flow shall be stopped, chlorination equipment shall be relocated at the head
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of the slug, and, as flow is resumed, chlorine shall be applied to restore the free
chlorine in the slug to not less than 100 mg/ L.
4. Industry Practice
To compare actual industry practice with AWWA C651 recommendations, a task
group member conducted an informal survey of numerous City Water
Departments. The survey was geographically broad and included utilities in
Seattle (WA), Fresno (CA), Chicago (IL), Minneapolis (MN), San Antonio (TX),
Savannah (GA) and Augusta (ME). It was learned that chlorine was by far the
disinfectant of choice. All three methods described in C651 (tablet, continuous
feed, and slug) are used, with the tablet method being the most popular because
it requires no additional equipment.
For the tablet method, AWWA C-651 recommends the use of an average
chlorine content of 25 mg/L for at least 24 hours. The utilities surveyed stated
that concentrations ranging from 25-150 mg/L were used for durations from 24 to
72 hours. Preferably, disinfection should be carried out overnight, however, not
on a day before the weekend or holidays
In the continuous feed method, the chlorine may be added as dissolved calcium
hypochlorite, sodium hypochlorite, liquid chlorine or dissolved chlorine gas.
Several opinions were given that dissolved chlorine gas offered the “best”
disinfection; however, environmental concerns and regulations have made this
option less desirable. The water utilities that were interviewed use concentrations
ranging from 25-60 mg/ L for durations of 24-72 hours.
The slug method is generally used in conjunction with the tablet method. After
the tablet method is completed and flushed, a heavily concentrated slug of
chlorine is added to the main and slowly forced through the system. The
concentration of the slug is monitored and more chlorine is added if the free
chlorine residual drops below 50 mg/ L. Several of the utilities use this method at
concentrations of 300-500 mg/L. Disposal and treatment of the heavily
chlorinated water can become a problem with this procedure.
5. Test Results
To evaluate the effects of chlorine exposure on PE water pipe during typical
disinfection, physical properties of selected PE pipe samples were studied.
Properties of pipe specimens exposed to chlorine were compared to properties of
the same specimens that were not exposed. The test methods and the results of
these tests are presented herein.
5.1 Quick Burst
Test Objective: To determine if the chlorine exposure had a detrimental effect on
the burst strength of the pipe. Testing was conducted on pipe specimens filled
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with a 185-ppm chlorine water solution and conditioned for 72 hours at room
temperature. Control specimens were also tested. The controls were not filled
with tap water until tested.
Test Method: Quick burst testing was then conducted in accordance with ASTM
D-1599, Standard Test Method for Short-Time Hydraulic Failure Pressure of
Plastic Pipe, Tubing, and Fittings. Several specimens were prepared from each
sample. The specimens were 18” in length and sealed at each end with
Swagelok fittings. For each sample, half the specimens were filled with water
containing chlorine at 185 ppm, the other half were not filled until testing. The
specimens exposed to chlorine were then placed on a sealed manifold for 72
hours. The control specimens were conditioned in the same room as the chlorine
specimens for the same time period.
Description of Test Samples:
• 1: ½” SIDR 11.5 PE2306, ASTM D2239
• 2: ½” SIDR 11.5 PE3408, AWWA C901
• 3: ¾” SDR 9 PE3406, ASTM D2737
• 4: ¾” SDR 9 PE3408, ASTM D2737
• 5: ¾: SDR 9 PE 3408, ASTM D2737
Test Results and Data:
Burst Pressures, psi
Sample Without Chlorine With Chlorine
1
545 530
510 530
610 600
2
600 590
620 610
800 960
3
800 810
810 830
1040 1030
4
990 960
960 990
5
850 830
840 850
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Failures for samples 2, 3, 4 and the chlorine specimens of sample 5 were in a
ductile mode with ballooning prior to rupture. Failures for samples 1 and the nonchlorine
specimens of sample 5 were in the slit mode.
Conclusion: The burst strength of Polyethylene (PE) pipe exposed to 185 mg/L
chlorine for 72 h, showed no apparent difference from that filled with tap water.
5.2 Sustained Hydrostatic Burst
To further evaluate the possible effects of chlorine exposure on actual pipe
samples, sustained pressure testing per ASTM-D1598, Standard Test Method for
Time-to-Failure of Plastic Pipe Under Constant Internal Pressure, was conducted
on samples of the PE3408 pipe. Testing was performed at 176°F to accelerate
any adverse effects on performance. Two different conditioning times were used:
72 hours and 240 hours. Further details of the test and results are listed below.
Set 1
Conditioning:
72 hours
73+3°F
321 mg/ L free chlorine at start of conditioning
Control samples were not exposed to any chlorine during conditioning
Testing:
176+3°F
Specimen Hoop Stress Conditioning Failure
1 600 psi Chlorine 916 hr (no failure)
2 600 psi Control 916 hr (no failure)
3 600 psi Chlorine 916 hr (no failure)
4 600 psi Control 916 hr (no failure)
5 600 psi Chlorine 916 hr (no failure)
6 600 psi Control 916 hr (no failure)
7 750 psi Chlorine 953 hr (no failure)
8 750 psi Control 953 hr (no failure)
9 750 psi Chlorine 953 hr (no failure)
10 750 psi Control 953 hr (no failure)
11 750 psi Chlorine 953 hr (no failure)
12 750 psi Control 953 hr (no failure)
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Set 2
Conditioning:
240 hours
73+3°F
305 mg/ L free chlorine at start of conditioning:
210 mg/L at 120 hrs, refilled;
309 mg/ L at refilled (120 hrs);
217 mg/ L at 240 hrs
Control samples were not exposed to any chlorine during conditioning
Testing:
176+3°F
Specimen Hoop Stress Conditioning Failure
1 600 psi Chlorine 420 hr (no failure)
2 600 psi Control 420 hr (no failure)
3 600 psi Chlorine 420 hr (no failure)
4 600 psi Control 420 hr (no failure)
5 600 psi Chlorine 420 hr (no failure)
6 600 psi Control 420 hr (no failure)
7 750 psi Chlorine 446 hr (no failure)
8 750 psi Control 446 hr (no failure)
9 750 psi Chlorine 446 hr (no failure)
10 750 psi Control 446 hr (no failure)
11 750 psi Chlorine 446 hr (no failure)
12 750 psi Control 446 hr (no failure)
Although somewhat limited, the results of sustained hydrostatic burst testing do
not suggest any significant effect of chlorine exposure on long term performance.
Unfortunately, testing could not be continued longer because of the need for the
test stations being used. Ideally, data at sufficient pressures and times to permit
calculation of Hydrostatic Design Basis would provide a better estimate of long
term performance.
It should be noted that all of the specifications for polyethylene water pipe (ASTM
D2239, D3035, D2447, etc.) contain a sustained pressure requirement. The highdensity
material used for this study would be required to pass a 176°F sustained
pressure test of 60 hours (minimum) at 725 psi or 150 hours (minimum) at 580
psi. It can be seen that all of the samples used in this study easily met these
requirements.
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5.3 Tensile and Elongation
A standard PE 3408 resin was compression molded in accordance with
Procedure C of ASTM Method D1928. The molded specimens were randomly
divided into two groups. One group was placed in a glass vessel containing a
200-ppm chlorine water solution at room temperature. Measurements of free
chlorine were made every other day and sodium chlorite solution added to
maintain the 200-ppm target. The second group of specimens was exposed to
“tap water” with a measured chlorine content of approximately 1 ppm. Samples
were then removed periodically from the vessel and tested for tensile strength at
yield and elongation at break in accordance with ASTM D638. A grip separation
rate of 2-in/ minute was used. It should be noted that, because of the large
number of samples required, only two specimens were tested at each of the time
periods noted. This undoubtedly contributed to the scatter seen in the results.
Based on the early test results, exposure times were extended well beyond the
original intent in an attempt to detect any possible downward trend. Exposure
testing was carried out to 1176 hours without any indications of adverse effects.
Test results are summarized below:
Hours
Tensile Strength (Break) (Elongation Break)
Chlorine Water Chlorine Water
24 4210 805
48 4141 796
72 4180 748
168 4285 4262 760 762
336 4249 4484 731 779
504 4314 4902 730 756
672 4753 805
840 4125 4329 793 752
972 4107 721
1008 4272 3990 781 788
1176 4310 803
5.4 Oxidative Induction Time
Because the chlorine disinfection process puts polyethylene pipe in contact with
a strong oxidizer, it was decided to monitor the effect on chlorine exposure on
thermal stability. Oxidative Induction Time as measured by a differential scanning
colorimeter (DSC) was used as an indication of thermal stability. The same
compression molded samples (PE3408) and chlorine solution (200 ppm) used for
tensile strength and elongation measurements in Section 5.4 were used in this
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study. Again, exposure times were extended well beyond the original intent in an
attempt to detect any possible downward trend. Exposure time and OIT results
are summarized below:
Hours
OIT, minutes
Chlorine
Water
24 17.2 17.2
48 18.8 17.9
72 16.2 16.8
168 18.8 19.2
336 19.9 20.1
504 16.3 16.6
672 19.5 20.1
840 19.0 20.2
1008 17.8 16.9
1176 17.4 16.4
1512 17.9 17.5
1872 18.2 17.9
2400 18.4 17.6
2568 17.9 17.6
It is apparent that no downward trend is evident even after 2,500 hours of
exposure. Although some variation in the individual measurements is visible,
there does not appear to be a significant difference between the chlorine and
water exposures.
5.5 High Speed Tensile Impact
A new high-speed tensile impact test (the McSnapper) has been gaining
increased popularity in the industry to evaluate the integrity of heat fusion joints.
It was believed that the test might be sensitive enough to detect any adverse
effect of chlorine exposure on the fusion joint. Two samples of PE3408 pipe were
prepared by heat fusing two segments each together. One sample was capped,
filled with tap water and stored at room temperature (75°F) for 30 days. The other
sample was capped, filled with 200-ppm chlorine water and stored for 72 hours.
No internal pressure was applied to either sample at the end of the exposure
periods; the samples were drained and flushed with distilled water.
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Four sample coupons were cut from each sample. The results of measuring high
speed tensile with impact device are summarized below.
Energy, in-lbf
Sample Number Water Chlorine
1 240.6 247.6
2 256.8 273.8
3 300.3 211.3
4 260.0 305.5
It was concluded that there was no appreciable difference in tensile strength
between the two samples.
5.6 PENT Testing
One of the major concerns for long term performance of polyethylene pipe (for
both water and gas) continues to be its resistance to slow crack growth. Although
the standard method for determining Hydrostatic Design Basis (ASTMD2837)
has provided an excellent estimate of this parameter; it is admittedly a lengthy
and labor intensive procedure. Over the years, a number of tests have been
developed to provide an accelerated estimate of resistance to slow crack growth.
These include Test Method for Environmental Stress-Cracking of Ethylene
Plastics (D1693) and Test Method for Determination of Environmental Stress
Crack Resistance (ESCR) of Polyethylene Pipe (F1248). However, as
polyethylene materials have improved over the years, the time to failure using
these ESCR tests has increased dramatically. In the continuing search for a
quicker slow crack growth test, two more recent tests have emerged. One is the
PENT Test that is officially designated as ASTM F1473 - Standard Test Method
for Notch Tensile Test to Measure the Resistance to Slow Crack Growth of
Polyethylene Pipes and Resins. The other is the British Gas Notch Test which
has been adopted by ISO as FDIS 13479-Polyethylene Pipes for the
Conveyance of Fluids-Determination of Resistance to Crack Propagation Test
Method for Slow Crack Growth on Notched Pipes (notch test). It has also been
added to ASTM as F1474. Both of these tests have demonstrated promise in
predicting resistance to slow crack growth in a reasonable time frame.
It has become apparent that the European/ World community has selected the
notched pipe test to measure resistance to slow crack growth while the U.S. pipe
industry has selected the PENT Test. A number of Task Groups have been
formed in both PPI and ASTM to refine the test method and to build a data base
for establishing acceptance values for the various end use applications. For
those reasons, a standard PE 3408 pipe material was compression molded and
milled to size following the procedure outlined in ASTM F1474. A total of six
specimens were prepared from the same resin sample. Two were notched and
used as the control; two were exposed to 200-ppm chlorine water and then
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notched. The third set were notched and then exposed to 200-ppm chlorine
water. Constant Tensile Load testing at 80° (PENT Test) was then performed.
Results are summarized below:
Control
72 hr Cl, then notched
Notched, then 72 hr Cl
PENT Values, hr
68.36
70.44
65.44
70.61
68.82
68.27
PENT Average, hr.
69.40
68.03
67.72
All of the above values would be considered to be within the accuracy of the test
method. Chlorine exposure did not appear to adversely affect test life of the PE
resin.
6. Other Experience
Studsvik Material AB in Sweden has done a number of studies on the long-term
behavior of polyolefin pipes used in hot water environments. One - “Long-Term
Properties of Hot-Water Polyolefin Pipes - A Review “ by U.W. Gedde, J. Viebke,
H. Leijstrom and M. Ifwarson is of particular interest. A collective view of the
changes in antioxidant concentration profiles and molecular/ physical structure
accompanying hot-water exposure is presented. A presentation is also made of
current lifetime extrapolation methods. Studsvik performs long-term hydrostatic
burst testing using chlorine for clients on a proprietary basis.
The effect of chlorine on PE piping in water distribution service has been a
concern in Japan for many years. However, the major part of their investigations
has been with piping made from lower density PE materials and used in water
distribution. A test method on blistering caused by chlorine contact has been
written and acceptance levels for the degree of blistering have been established.
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7. Chlorine Dissipation Rate
To estimate the dissipation rate of chlorine, without the addition of fresh chlorine,
seven pipe samples were filled with water originally at 321-mg/ L free chlorine.
The samples were then capped with mechanical steel fittings and sealed. At
each of the times shown below, one sample was opened and the water
immediately analyzed for free chlorine.
Start
321 mg/L
24 hours 271 mg/L
48 hours 227 mg/L
72 hours 216 mg/L
96 hours 168 mg/L
8 days 140 mg/L
14 days 58 mg/L
8. Conclusions/ Recommendations
The testing performed in this study indicates that chlorine disinfection, when
conducted within the guidelines of AWWA-C651, does not have a significant
adverse affect on the performance of PE pipe. No indications of any downward
trends in the exposure tests were evident.
9. References
ASTM D-1599, Standard Test Method for Short-Time Failure Pressure of Plastic
Pipe, Tubing and Fittings.
ASTM D-1598, Standard Test Method for Time-to-Failure of Plastic Pipe Under
Constant Internal Pressure.
ASTM D-638, Test Method for Tensile Properties of Plastics
ASTM D-2837, Test Method for Obtaining Hydrostatic Design Basis for
Thermoplastic Pipe Materials.
ASTM D-1693 Stress-Cracking of Ethylene Plastics
ASTM F-1248, Test Method for Determination of Environmental Stress Crack
Resistance (ESCR) of Polyethylene Pipe.
ASTM F-1473, Standard Test Method for Notch Tensile Test to Measure the
Resistance to Slow Crack Growth of Polyethylene Pipes and Resins.
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AWWA C-651, Disinfecting Water Mains
AWWA C-901, Polyethylene (PE) Pressure Pipe and Tubing, ½ in Through 3
inch, for Water Service
AWWA C–906, Polyethylene (PE) Pressure Pipe and Fittings, 4 in. (100 mm)
through 63 in. (1,575 mm), for Water Distribution and Transmission
ISO FDIS-13479, Polyethylene Pipes for the Conveyance of Fluids -
Determination of Resistance to Crack Propagation Test Method for Slow Crack
Growth on Notched Pipes
U.W. Gedde, J. Viebke, H. Leijstrom and M. Ifwarson, Polymer Engineering and
Science, 34, 24 (1994).
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